1. Field of the Invention
This invention relates to an arrangement for an electronic device for electrically coupling a component to a circuit board. The invention also relates to an electroacoustic transformer having a unique structure. Furthermore, the invention relates to a wireless communication device comprising an arrangement for electrically coupling a component to a circuit board. In addition the invention relates to a method for the electrical coupling of a component to a circuit board in an electronic device.
2. Description of the Prior Art
In a known manner, various electronic devices incorporate printed circuit boards (PCB) which are provided with electronic circuits, such as integrated circuits (IC), to control the operation of the devices and which contain printed conductive patterns to couple the circuits electrically to each other for the transmission of signals. These circuit boards can also be multilayer printed circuit boards, wherein the wirings extend between two board layers and the connection through one or several board layers is implemented with through holes.
Said devices often also incorporate components which must be installed separately and electrically coupled to the circuit board and further to the circuits fixed on the circuit board. For example in wireless communication devices, such as mobile phones, such components are electroacoustic transformers which convert an electrical signal to an acoustic signal, normally to an audible sound, or vice versa. Transformers include earpieces, microphones, buzzers, and various speakers. It is typical that the devices comprise several cover parts which are fitted with the circuit board and equipped with the separate components and which cover parts are fixed to each other during the assembly. In the fixing, an electrical coupling must be produced between the conductive patterns of the circuit board and the components, to make the operation of the device possible.
In patent publication EP 0 490 214 B1, an electrical contact between a circuit board and an electroacoustic transformer is produced by means of a spring-like means, i.e. a contact spring. The contact spring is fixed with jaw to the contact of the transformer, and it also touches the circuit board, normally a conductor, such as a microstrip, arranged in the circuit board. Patent publication EP 0 567850 B1 presents a solution in which a part operating in a spring-like manner is fixed by penetration into the circuit board, and a tag in the transformer is fitted between jaws. In this solution, the transformer and the spring-like part are in a fixed position in relation to each other and the circuit board; furthermore, careful position of the transformer is required in the assembly. Also known is a connector presented in publication WO 97/29528 for coupling a transformer electrically to a circuit board. This solution, however, applies a separate connector component fixed to the circuit board and comprising spring-like means which further constitute the contact with strips arranged in the transformer. The spring-like means are further coupled to the conductors of the circuit board. Also in this solution, the transformer and the connector are in a fixed position in relation to each other and the circuit board.
According to the patent publication EP 0 490 214 B1, the transformer normally comprises two separate connectors, i.e. contacts, implemented for example with contact springs, for the transmission of two different signals. Thus, also the conductors of the signals must be electrically separated from each other on the circuit board. Typically, a circular transformer is allowed to rotate into different positions when it is installed in its position in a nest fitted in the device and its cover. For this reason, the first contact spring is usually located centrally in the transformer and the second contact spring is located closer to the edge of the transformer. For the second contact spring, the circuit board is normally equipped with a circular contact surface arranged in the form of an endless ring, for example a strip conductor with an even width. For the first contact spring, the circuit board is normally equipped with a circular second contact surface, e.g. a strip conductor, formed in the center of the circular contact surface.
To bring the second contact surface into an electrical contact with a third strip conductor fitted on the circuit board past the first contact surface, a fourth strip conductor is formed on the second surface or between the board layers of the circuit board, connected e.g. by through-holes with the second contact surface and the third strip conductor. The second contact surface can be directly connected to something, for example a fifth strip conductor, which is fitted together with the annular and circular contact surfaces on the surface of the circuit board.
The above-presented case involves, however, the problem that the circuit board must be provided with strip conductors on at least two different levels, which makes the manufacture of the circuit board considerably longer and more complicated; moreover, one must use more expensive multilayer printed circuit board, and the alternatives for the material of the circuit board are limited. Also known is a foil-like flexible printed board which is made of e.g. polyamide and which consists of a flexible base material. Moreover, a so-called flexible conductor cable is known, which consists of a flexible base material and conductors on its surface. The material of the conductive patterns is generally a copper film. In a part of the flexible material, it is possible to form several layers, but in this case this part is not resistant to bending, which restricts the placing of the circuit board. It is possible to construct several layers in only part of the flexible circuit board, but this makes the manufacturing process considerably more complicated and longer in time.
In a known manner, attempts have been made to overcome the above-presented problem in such a way that the annular first contact surface is provided with a point of discontinuity, such as an opening, through which the second contact surface is coupled to other strip conductors, e.g. by means of said fourth conductor. It is thus possible to use contact surfaces and strip conductors formed on only one surface of the circuit board. This solution sets, however, special requirements on the installation, because the second contact spring which is intended to make a contact with the first contact surface must not make a contact with said fourth conductor or hit a location with an opening or insulated area in the first contact surface. In many cases, a transformer can be fitted in the cover part of the device, or a like, in only one position, which, however, restricts the placement of the contact surfaces on the circuit board and the use of different transformer models. Furthermore, the final position must also be taken into account at an early stage in the manufacture of the cover parts and/or the transformers. This will result in problems of compatibility and mounting faults, or malfunction of the device will be due to a displacement of the transformers during the use.
The above-mentioned fourth strip conductor can also be conveyed above or underneath the endless first contact surface, but in this case several layers and insulators must be formed on the surface of the circuit board to isolate the strip conductor and the contact surface from each other and/or from the second contact spring, which makes the structure and its manufacture more complex. If the fourth strip conductor is conveyed above the contact surface and isolated, an opening of the above-mentioned kind is formed again in the first contact surface.
It is an aim of the present invention to eliminate the above-mentioned drawbacks and to produce an arrangement which limits the transformer, the mounting of the transformer, as well as the manufacture and position of the contact surfaces as little as possible, preferably to couple an electroacoustic transformer and the circuit board electrically to each other.
The central principle of the invention is that the transformer is provided with at least two contact springs which are, in view of the use and the transmission of the electrical signal, alternative to each other, for the above-described annular contact surface. The contact springs are fitted in such a way that irrespective of the rotary position of the transformer and irrespective of the location of the discontinuity of the annular contact surface, at least one contact spring always forms a connection, i.e. a contact, to the annular contact surface. At the same time, the other contact springs hit e.g. opening locations or insulators but not a contact with the other contact surfaces. The other contact springs can also be located on an insulator which is placed above another contact surface or strip conductor.
The invention gives considerable advantages to the prior art. The rotary position of the transformer can be even completely free, if the contact springs are placed in a centralized and annular way. In case there are several alternative predetermined positions that can be selected for the transformer, the position can still be selected from these even completely freely. The mounting will be considerably easier and faster, and the devices or transformers do not need to be equipped with forms or parts which force the transformer in a desired position. Consequently, it is only necessary in the device to secure that the component, such as a transformer, and the contact surfaces of the circuit board face each other, e.g. centrally, and at a desired distance from each other. With the invention, the direction of the opening in the contact surface can be selected even completely freely, because the rotary position of the transformer does not affect the functionality of the device. Thus, the direction of the opening on the circuit board can be varied among different devices according to the need.
It is a particular advantage of the invention that, with the arrangement, it is also possible to use a flexible circuit board whose one surface is provided with the necessary contact surfaces, insulation layers and strip conductors. The use of a flexible circuit board facilitates particularly the construction of small electronic devices and increases the possibilities of space utilization for reducing the size of the device further, if necessary. Another advantage is that even though the transformer is arranged according to the invention, its functioning is still possible also with most previously known circuit board arrangements and designs of contact surfaces. Thus, even new transformer models are compatible with old devices.
Another particular advantage is easy expansibility, wherein it is also suitable for transformers which require e.g. three or more separate signal connections and contacts to the contact surfaces of the circuit board, which connections and contacts are electrically separated from each other. Thus, the circuit board is provided with a central round continuous contact surface, around the same an annular contact surface cut with an opening, and further around this an annular contact surface cut with an opening. The cutting points are used to lead the strip conductors of the innermost contact surfaces which are covered with an insulator, if necessary, to form a connection elsewhere in the circuit board.
The number of contact springs of the component for each annular contact surface depends on the length of the circumference of the surface, particularly its sector angle, wherein when the contact surface comprises one opening and covers at least half of the periphery of a circle (sector angle more than 180 degrees), there must be at least two contact springs. When the contact surface covers at least one third of the periphery of a circle (sector angle more than 120 degrees), there must be at least three contact springs. When the contact surface comprises additional openings, each contact spring must be provided with at least one pair at a distance which is greater than the width of the opening. On the other hand, the distance of the springs must be different from the distance of the openings. Thus, at least one contact spring of the pair always forms a contact with the surface.
For example a strip-like or wire-like contact spring can be, alternatively, arranged or formed so wide that its contact extends from the opening to the contact surface. The contact spring can also be designed to have two or more points with the shape of e.g. a V or U, each point forming a contact and the distance between the points being greater than the size of the opening. This has the advantage that the transformer does not need to be connected to several contact springs or provided with several strip-like or pin-like connectors for the contact springs. The second point is also used for backup.
As an advantage of the invention, it can also be particularly mentioned that the contact surfaces can also be provided in the transformer and the contact springs can be placed on the circuit board by grouping according to the invention, which further increases the various structural alternatives. The transformer and the circuit board can also be fitted with both contact surfaces and contact springs. The different solutions yield the significant advantage that in each case, it is possible to select very freely the economically and technically most suitable alternative.
Furthermore, the invention can be applied in the coupling of other electrical components, such as light emitted diode (LED) and several coupling elements, for example press-button switches. By means of the invention, also these components can be arranged to be symmetrical, particularly circular, and to have a free mounting position, because the contact can be secured in the different rotary positions of the component. By means of the invention, it is also possible to eliminate the selection of the position of present symmetrical components to be located in different positions, or arrangements for guiding the position, to make the assembly faster and simpler. The invention is thus particularly well suited for assembling components by machine.